Vinyl esters of epoxides and unsaturated acid anhydrides are used as photo-curing prepolymers and as surface coating resins having good electrical properties, high adhesion on most substrates and good chemical resistance. However, there is a need for highly reactive vinyl esters having in addition to said good properties, also good temperature stability and better chemical resistance.
Reaction products of epoxide compounds with unsaturated acid anhydrides and/or carboxylic acids are known per se. However, in these products, the epoxide groups are only partially esterified with the epoxide groups being substituted by xcex2-hydroxy vinyl ester groups. JP-A-02077417 discloses, for example, coating agents for metal containers, which comprise a binding agent which is converted by conversion of 90-99.95% by weight of an aromatic epoxy resin with 0.05-10% by weight of acrylic and/or methacrylic anhydride.
DE-A-42 09 248 describes graft polymers, in which in a first step, epoxy resins are heated with small amounts of acrylic and/or methacrylic anhydride and these products are then reacted with other ethylenically unsaturated compounds. From JP-A-08259663 are known radiation-curable vinyl esters, in which in a first reaction step, epoxy resins are reacted with 0.1-0.8 mole of acrylic and/or methacrylic anhydride and with 0.2-0.9 mole of unsaturated carboxylic acid per mole of epoxide group. Then, conversion of these reaction products or the xcex2-hydroxy groups of these vinyl esters with multivalent acid anhydrides is effected.
It is an object of the invention to provide vinyl esters with good temperature stability and improved chemical resistance and a process for their preparation.
It is another object of the invention to provide improved surface coating resins and photo-curing prepolymers.
These and other objects and advantages of the invention will become obvious from the following detailed description.
The vinyl esters of the invention are produced by reacting at least one epoxide compound with at least one carboxylic acid anhydride containing ethylenically unsaturated groups, the epoxide groups being substantially substituted by two vinyl ester groups. It has been found that vinyl esters substantially free of xcex2-hydroxy groups are obtained if the epoxide compounds are reacted with stoichiometric amounts of ethylenically unsaturated carboxylic acid anhydrides.
For example, in the reaction of bisphenol A or bisphenol F diglycidyl ethers with acrylic acid or methacrylic acid in stoichiometric quantities with respect to the epoxide groups, vinyl esters are obtained with an equivalent weight of 250 to 300 g of resin/double bonds. In the corresponding reaction with acrylic acid anhydride or methacrylic acid anhydride, vinyl esters are formed with an equivalent weight of 170 to 200 g of resin/double bonds.
In the products obtained by the invention, the epoxide groups are substantially substituted by two vinyl ester groups. These vinyl esters exhibit the same good property profile as the known vinyl esters, but yield an increased cross-linkage density after curing which leads to higher resistance to chemicals and better temperature stability. The vinyl esters with high cross-linkage density of the invention surprisingly have a markedly lower viscosity than vinyl esters comprising simple xcex2-hydroxy groups. They are useful for surface coating, resins, photo-curing components in coating agents and as binding agents in chemical reaction resin materials, particuarly for chemical anchoring agents.
For example, in a varnish formulation at identical monomer fraction, there is obtained a lower processing viscosity, which means, to attain the same final viscosity, the fraction of monomers or solvents can be decreased. This leads yet again to a further increase of the resistance to chemicals and better temperature stability. A further surprising advantage comprises that the vinyl esters of the invention with high cross-linkage density, nevertheless, have an improved storage life. They can be stored at ambient temperature for up to 52 weeks without a substantial increase of their viscosity being observed.
Examples of epoxide compounds for the production of the vinyl esters of the invention are all monomeric or oligomeric compounds, glycidyl ethers, glycidyl esters or N-glycidyl compounds with one or more epoxide groups, known per se. Preferred are epoxide compounds with two and more epoxide groups in the molecule, particularly diglycidyl ethers of bisphenols as well as glycidyl ethers of novolaks based on phenol, cresol or bisphenols.
In principal, as ethylenically unsaturated carboxylic acid anhydrides can be used all carboxylic acid anhydrides of monocarboxylic acids, which have one or more ethylenically unsaturated groups. The preferred anhydrides are acrylic acid anhydride and methacrylic acid anhydride.
The reaction of the epoxide compounds with the ethylenically unsaturated acid anhydrides takes place in a manner known per se by combining the components in corresponding quantities, using a solvent if appropriate, a catalyst known per se and a stabilizing agent acting as a radical interceptor, such as, hydroquinone, p-benzoquinone, methylhydroquinone, catechol and the like.
The catalyst is selected from the groups of metal salts, known per se, such as dibutyl tin dilaurate, tin octoate, phosphorus compounds, such as triphenyl phosphine or ethyl triphenyl phosphonium bromide, tert. amines, such as dimethylaminopyridine or benzyl dimethylamine or quaternary ammonium compounds, such as tetraethyl ammonium bromide. The particular reaction mixture is then heated for several hours at temperatures in the range of 80 to 120xc2x0 C. In this reaction oxygen, or a gas comprising oxygen, is preferably conducted through the reaction mixture to prevent polymerization.
In the conversion of hydroxyl group-free epoxide compounds with the ethylenically unsaturated acid anhydrides, a small amount of a carboxylic acid is preferably added to accelerate the start of the esterification reaction. Preferred are ethylenically unsaturated carboxylic acids, in particular acrylic acid and/or methacrylic acid. With increasing amounts of added carboxylic acid, on the one hand, the start of the esterification reaction is accelerated, on the other hand, however, the content of vinyl ester groups is decreased. Balancing these two criteria against one another, therefore the amount of the added carboxylic acid is selected so that it is within the range of up to 0.1 mole, preferably up to 0.05 mole, more preferably up to 0.01 mole per mole of epoxide groups. The amounts of ethylenically unsaturated acid anhydrides used in this case must be correspondingly reduced so that per mole of epoxide group are used 0.9 to 1 mole of ethylenically unsaturated acid anhydride and 0.1 to 0 mole of carboxylic acid, preferably 0.95 to 1 mole of ethylenically unsaturated acid anhydride and 0.05 to 0 mole of carboxylic acid, and, most preferably 0.99 to 1 mole of ethylenically unsaturated acid anhydride and 0.01 to 0 mole of carboxylic acid.
If the epoxide compounds used comprise hydroxyl groups, such as is the case with epoxy resins which are produced by reaction of bisphenol with epichlorhydrin and subsequent advancement reaction, omission of a starter acid is preferred.
The processing of the reaction mixture also takes place in a manner known per se by carefully distilling off the solvent which optionally had been used, and, if appropriate, by adding a further stabilizing agent. As a rule, liquid products are obtained which are curable by radiation, heat or by means of catalysts. Due to their properties, they are preferably used as surface-coating resins, as photo-curing components in coating agents as well as binding agents or binding agent component in chemical resin materials, in particular such for the production of chemical anchoring means.
In the following examples, there are described several preferred embodiments to illustrate the invention. However, it is to be understood that the invention is not intended to be limited to the specific embodiments.